Two New Ergosterol Derivatives from the Basidiomycete Cortinarius glaucopus

Two new sterols 1 and 2 and five known ones 3 - 7 were isolated for the first time from the fruiting bodies of Cortinarius glaucopus. Their structures were established by 1- and 2D-NMR spectra and HR-FABS-MS. The relative configuration of 1 was firmly determined by comparison of the observed ¹ H-¹ H couplings and NOESY correlations, with those predicted for the computed geometries of the conformers. Calculations were performed by means of DFT with the B3LYP functional at 6-31 + G(d,p) level of theory, in CHCl₃ as the solvent. The structures of the new ergosterol derivatives, called glaucoposterol A (1) and B (2), were thus established as (3S,5R,7R,10R,13R,17R,20S,22R,23R,24R)-5,6-epoxy-3,7,23-trihydroxystrophast-8-en-14-one and (22E,3S,5S,9S,10R,13R,17R,20R,24R)-3,5-dihydroxyergosta-6,8(14),22-trien-15-one, respectively. Moreover, the configuration of known strophasterol C (3) was determined as (3S,5R,6S,7R,10R,13R,17R,20S,22S,24R). Glaucoposterol A (1) and strophasterol C (3) represent the second finding in nature of steroids with the rare strophastane skeleton.